This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-350443, filed Dec. 9, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an image projection system and, more particularly, to a calibration technique therefor.
A back projection type display apparatus has been available, which uses a transmission type screen and projects an image from the opposite surface side (rear surface side) to the observation surface side (front surface side) onto the screen by using a projector. As an advanced form of this system, a high-resolution back projection type large-screen display apparatus is also available, which projects a plurality of images from a plurality of projectors onto a screen to display them as one image.
In this back projection type large-screen display apparatus, since a plurality of projected images are joined into one image, the following measures must be taken.
First, this apparatus requires measures to correct distortion of each projected image. For this purpose, there have been provided a method of adjusting the angle of each projector to prevent each projected image from being distorted, and a method of giving an original image distortion that cancels out distortion of each projected image. Either of the methods requires means for detecting information about distortion of each projected image. For this purpose, a method using a digital camera and a method using a sensor placed on the screen have been proposed.
Second, this apparatus requires measures to perform correction associated with joining of projected images. For this purpose, a technique of smoothly joining images by overlapping adjacent images each other has been proposed. This technique, however, requires a means for detecting information about overlapping areas. For this purpose, a method of extracting a correction value from an image captured by a digital camera has been proposed.
Third, this apparatus requires measures to perform color correction of each projected image. For this purpose, a method has been proposed, in which a standard image is projected from a projector onto a screen, the overall projected standard image is captured by a digital camera, a correction value is extracted from the captured standard image, and color correction is performed by using this correction value.
Correction value acquiring operation (adjustment processing) for performing the above series of correcting operations will be referred to as calibration. This calibration is performed when the image projection system is influenced by age-based change as well as system installation.
The conventional image projection system is, however, designed to execute calibration while placing the digital camera on the front surface side of the screen. For this reason, in executing calibration, a user must adjust the installation position, angle, focus, and the like of the digital camera, imposing a heavy load on the user in adjustment.
The digital camera may be fixed in advance on the rear surface side of the screen to reduce the load of adjustment on the user in executing calibration. In this arrangement, however, an image on the screen is captured in a direction different from the direction (front surface side) in which the user sees the image projected on the screen, and hence it is difficult to perform appropriate adjustment.
The present invention has been made to solve the above problems, and has as its object to provide a back projection type image projection system which allows appropriate adjustment when the digital camera used for calibration is installed on the rear surface side of the screen.
According to the present invention, there is provided an image projection system comprising projection means for projecting an image on a transmission type screen from a rear surface side of the screen, standard image information generating means for generating standard image information of a standard image, image capturing means for capturing an image on the rear surface of the screen from an inside of a casing in which the projection means is housed, the image capturing means capturing the standard image projected onto the screen from the projection means, which receives the standard image information from the standard image information generating means, removing means for removing influences of external light from the standard image projected from the projection means onto the screen, correction value computing means for computing a correction value on the basis of image information of the standard image from which the influences of the external light are removed by the removing means, correction value storage means for storing the correction value information obtained by the correction value computing means, and correction means for correcting image information from a picture signal source by using the correction value information stored in the correction value storage means, and supplying the corrected image information to the projection means.
In the above image projection system, the removing means may have a function of blocking the external light that reaches the image capturing means through the screen.
In the above image projection system, the removing means may have a computing function of removing the influences of the external light on the basis of image information obtained by capturing an image on the screen by using the image capturing means while the standard image is projected from the projection means onto the screen and image information obtained by capturing an image on the screen by using the image capturing means while the standard image is not projected from the projection means onto the screen.
The above image projection system may further comprise means for storing information based on image information obtained by capturing an image on the screen from the rear surface side of the screen while the standard image is projected from the projection means onto the screen and image information obtained by capturing an image on the screen from the front surface side of the screen while the standard image is projected from the projection means onto the screen.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.